An article of footwear may include a sole and an upper that form a cavity, or foot compartment, in which a wearer places his or her foot when the article of footwear is donned and worn. The sole of the footwear engages the bottom of the wearer's foot and separates the foot from the ground. The sole often consists of one or more layers of materials, including leather, rubber, foam, and/or plastics that provide shock absorption and support to the wearer's foot. The upper extends outwardly from an outer periphery of the sole and covers at least a portion of the foot.
Footwear such as dress shoes, athletic footwear, work boots, hiking boots, and others are worn for a variety of applications which require a significant workload in terms of duration of wear or impact. Such footwear, particularly heeled footwear, includes a rigid shank that extends from a heel region of the sole assembly to the forefoot region of the sole assembly. Such a conventional shank is typically secured to an outsole portion of the footwear and sole, above which a midsole portion and/or footbed are positioned. The sole assembly and shank may provide for limited padding or shock absorption in the course of a wearer's gait.
During walking or running, the human foot transfers energy (e.g., in the form of force from the shock impact of the wearer's foot striking the ground with the sole between the foot and the ground) into the sole and further to the ground through the sole. A substantial portion of this energy is lost to the wearer, such as by being disbursed into the material of the sole at the area of contact. A portion of the energy that is not lost is returned into the foot of the wearer, but generally not in an advantageous manner. For example, some of the energy may be reflected back into the foot at the point of impact, which may cause discomfort, and potentially injury.